Jan 3 (Reuters) - Health insurer Cigna Group is in exclusive talks to sell its Medicare Advantage business to Health Care Service Corp for between $3 billion and $4 billion, a source familiar with the matter said on Wednesday.

Cigna and Health Care Service Corp did not immediately respond to Reuters' requests for comments.

The deal is expected to be announced in the coming days, if the talks do not fall apart, according to the source.

A sale could mark a change in Cigna's strategy for the Medicare segment as a vast majority of its revenue comes from its commercial business and pharmacy benefits division, which it bolstered with a $52 billion purchase of Express Scripts in 2018.

Reuters had reported in November that Cigna was exploring a sale of the business.

The Wall Street Journal first reported on Wednesday that Cigna was nearing a deal with Health Care Service.

(Reporting by Bhanvi Satija in Bengaluru and Anirban Sen in New York; Editing by Shinjini Ganguli)